Borehole production boosting system

ABSTRACT

Method and apparatus for assisting the flow of production fluid from a hydrocarbon wellbore ( 4 ) to a remote host facility ( 16 ) including a separation facility ( 6 ) situated close to the wellbore ( 4 ). Jetting fluid is supplied initially from the host facility ( 16 ) to a downhole jet pump ( 14 ) via the separation facility ( 6 ) for assisting the flow of production fluid from the wellbore ( 4 ) to the separation facility ( 6 ) where the resulting mixture enters one of two parallel gravity separation chambers ( 32 ). Separated jetting fluid ( 60 ) is recirculated to the jet pump ( 14 ) via a pump ( 38 ) and production fluid is routed to the host facility via a production pipeline ( 18 ). A jetting fluid supply pipe ( 20 ) can be of relatively small diameter and the production pipeline ( 18 ) does not have to be enlarged to accommodate jetting fluid returned to the host facility ( 16 ).

[0001] The present invention relates to a method and system for boostingthe supply of production fluid from a hydrocarbon wellbore or borehole.

[0002] When a reservoir of production fluid, such as oil, has a lownatural pressure and/or the fluid has a relatively high density, thereis a need to boost the pressure of the fluid at or near the reservoirsurface in order to achieve satisfactory production rates over the lifeof the reservoir.

[0003] One technique is to install a mechanical pump at a “downhole”location. Such pumps are typically electrically driven by a supply ofhigh voltage electricity provided from an associated host facility whichmay be tens of kilometres away. The provision of a high voltage powersupply for the pump motors is expensive. Furthermore, the pump isinstalled in a hostile environment which is hot and corrosive andrelatively inaccessible. Pump maintenance, which is almost inevitablyrequired, necessitates shutting the well in, thus interruptingproduction and possibly leading to restarting problems.

[0004] Another newer but existing technique is to install ahydraulically driven mechanical pump at a downhole location. Such pumpsare typically driven by a supply of pressurised water, the supply ofwhich is costly. Accessibility and maintenance problems apply asdiscussed above.

[0005] A different technique is to use a jet pump which is installed ata downhole location. Such a pump is supplied with pressurised jettingwater from the host facility which is mixed with the production fluid bythe jet pump. The resulting mixture is then conveyed back to the hostfacility. Additional costs arise from:

[0006] (a) the provision of a relatively large diameter high pressurepipe to supply the required quantity of pressurised jetting water to thewellbore;

[0007] (b) the requirement for a production pipe which is large enoughto accommodate the jetting water in addition to the production fluid;and

[0008] (c) separation of the jetting fluid from the production fluid atthe host facility.

[0009] An object of the invention is to provide a method and systemwhich overcome at least some of the above-mentioned disadvantages of theprior art.

[0010] Thus, according to the invention there is provided a method ofboosting production from a wellbore having a downhole jet pump and aremote host facility, the method comprising the steps of:

[0011] (a) providing a separation facility substantially closer to thewellbore than the host facility;

[0012] (b) providing means to deliver jetting fluid under pressure tothe jet pump;

[0013] (c) entraining wellbore production fluid with a flow of thejetting fluid in the jet pump and conveying the resulting mixture to theseparation facility;

[0014] (d) separating a majority of the jetting fluid from the mixture;and

[0015] (e) recirculating the separated jetting fluid back to the jetpump and entraining further production fluid therewith.

[0016] A single separation facility may provide jetting fluid to aplurality of and possibly all wellbores in a field.

[0017] Such a method may only require a relatively small diameterconduit for supplying a batch of jetting fluid to the separationfacility. Once adequate jetting fluid has been provided, this conduitwill no longer be required for this purpose. The pipe for conveyingproduction fluid from the separation facility to the host facility neednot be enlarged to cater for conveying the jetting fluid. Separation atthe host facility can be avoided as can the provision, from the host, ofa continuous flow of appropriately treated jetting fluid. The problemsassociated with a downhole mechanical pump discussed above are alsoavoided.

[0018] Preferably at least 90% and more preferably substantially all ofthe jetting fluid is separated from the mixture by the separationfacility in order to minimise the volume of fluid for conveyance to thehost facility and in order to minimise or preferably eliminate therequirement for additional jetting fluid from the host facility.

[0019] To maximise the savings resulting from the invention, theseparation facility is preferably situated at or close to the wellbores.

[0020] Preferably the separation facility includes a pump which is usedto pressurise the separated jetting fluid for assisting itsrecirculation.

[0021] Separation is preferably effected by gravity separation whichrelies on the jetting fluid and the production fluid having differentspecific gravities. Gravity separators are robust and suitable for usein a hostile location which may be difficult to access.

[0022] According to a second aspect of the invention there is provided asystem for boosting production from a wellbore situated remotely from ahost facility comprising a downhole jet pump, pressurising means forsupplying the jet pump with pressurised jetting fluid for forming amixture of jetting fluid and wellbore production fluid, separation meanssituated substantially closer to the wellbore than the host facilityincluding separator means for separating a majority of the jetting fluidfrom the mixture and recirculation means for delivering the separatedjetting fluid back to the jet pump for entraining further productionfluid.

[0023] Preferably the separator means includes at least one gravityseparation chamber.

[0024] In order to provide system redundancy to minimise the chance ofwellbore shut-in being required, preferably the separator means includesat least two separators for separating the mixture which are connectedin parallel with each other.

[0025] If the separator means includes throttling means arranged tocontrol flows of production fluid and jetting fluid out of theseparation chamber, control of the separation means can be easilyeffected, possibly from a control module situated at the separationmeans.

[0026] The invention will now be described by way of example only withreference to the accompanying schematic figures in which:

[0027]FIG. 1 shows a system suitable for putting the invention intopractice;

[0028]FIG. 2 shows the components of the system of FIG. 1 in greaterdetail; and

[0029]FIG. 3 shows a typical jet pump which will be situated at adownhole location in the systems shown in FIGS. 1 and 2.

[0030] In the following description the terms production fluid andjetting fluid will be employed. These will generally be oil and water(appropriately treated) respectively but could comprise other fluids ormixtures of fluids.

[0031] A system for putting the invention into practice is shown inFIG. 1. The system includes at least one wellhead tree 2 which routesfluids from a wellbore or lower production tubing 4 to a separationfacility 6 via a mixture pipe 8. A jetting fluid delivery pipe 10extends from the separation facility 6 to the wellhead tree 2 forsupplying jetting fluid to a downhole jetting fluid conduit 12 and henceto a downhole jet pump 14. The separation facility 6 is connected to ahost facility 16 by a production pipeline 18 and a jetting fluid supplypipe 20.

[0032] The components of the system will be described in detail withreference to FIG. 2.

[0033] The separation facility 6 includes first and second duplicatedseparating means 22 and 24 only the first 22 of which will be describedin detail. Only one separating means may be provided.

[0034] The mixture pipe 8 from the wellhead tree is connected to amixture inlet 26 which is connected via a failsafe valve 28 to an inlet30 of a separator chamber 32 containing a weir 34. A first outlet 36 ofthe chamber 32 is connected by a jetting fluid conduit 39 containing arecirculation pump 38, a throttle valve 40 and a non return valve 42 toa jetting fluid outlet 44 of the separation facility 6. A recirculationloop pipe 46, containing a non-return valve 48 and a pressurerestricting device 49, connects the jetting fluid conduit 39, downstreamof the recirculation pump 38, to the inlet 30 of the chamber 32.

[0035] A second outlet 50 of the chamber 32, situated on the oppositeside of the weir 34 to the first outlet 36, is connected via a throttlevalve 52 to a production fluid outlet 54 which is connected to theproduction pipeline 18 leading to processing equipment on the hostfacility 16.

[0036] The chamber 32 includes a level sensor 56 for determining thelevel of the interface between the production fluid 58 and jetting fluid60 within the chamber 32.

[0037] The jetting fluid supply pipe 20 from the processing equipment onthe host facility is connected to a jetting fluid inlet 62 of theseparation facility which is connected via a jetting fluid conduit 64,containing a non-return valve 66, to the jetting fluid outlet 44.

[0038] The host facility 16 includes apparatus (not shown) forprocessing production fluid 58 received through the production pipeline18 and a pump 68 for pumping jetting fluid (water treated as required toinhibit corrosion and hydrate formation problems etc. upon mixing withthe production fluid) to the separation facility 6.

[0039] The jet pump 14 shown in FIG. 3 is a conventional jet pump andwill accordingly only be described in outline. The jet pump includes anozzle 69 into which jetting fluid is fed (arrow A) from the jettingfluid conduit 12. Production fluid is routed to the jet pump via a lowerproduction tubing conduit 70 (arrow B) from the lower production tubing4, which opens into a low pressure entrainment region 72 at an outletend of the nozzle 68. An intake nozzle 74, also opening into the lowpressure entrainment region 72, is connected to upper production tubing76 for delivering a mixture of production and jetting fluid (arrow C) tothe wellhead tree 2 via the wellbore riser 76.

[0040] The operation of the system will now be described.

[0041] When production from the lower production tubing 4 needsboosting, for example because the well pressure is too low, a batch ofjetting fluid will be pumped by the host pump 68 down the jetting fluidsupply pipe 20 to the jetting fluid inlet 62 of the separation facility6 where it passes through the conduit 64 to the jetting fluid outlet 44and on through the jetting fluid delivery pipe 10 to the downholejetting fluid conduit 12.

[0042] The jetting fluid then enters the jet pump 14 (arrow A) and isforced through the nozzle 69 into the entrainment region 72 where alower pressure zone occurs causing production fluid to be drawn into thejet pump through the lower production tubing conduit 70 (arrow B) whereit mixes in the entrainment region 72 with the jetting fluid. Theresulting mixture then passes into the intake nozzle 74 and leaves thejet pump 14 up the upper production tubing 76 (arrow C).

[0043] On emerging from the wellhead tree 2, the mixture passes throughthe mixture pipe 8 and is conveyed to the inlet 30 of the chamber 32 viathe mixture inlet 26 and the failsafe valve 28. Upon entering thechamber 32, as a consequence of their different specific gravities, thedenser jetting fluid 60 (water) occupies the region to the left of theweir 34 (as shown in FIG. 2) and the less dense production fluid (oil)passes over the weir 34 into the region to the right thereof. Once thelevel sensor 56 detects that the interface between the jetting fluid 60and the production fluid 58 has reached the level shown in FIG. 2 (i.e.partway up the weir) the supply of jetting fluid from the host facilitywill be halted. Thereafter, jetting fluid 60 is drawn from the chamber32 by the recirculating pump 38 and routed to the jetting fluid outlet44 via the jetting fluid conduit 39 from where it travels on to the jetpump and recombines with further production fluid as described above.Meanwhile, production fluid leaves the chamber 32 via the second outlet50 (as a consequence of chamber pressure) and passes via the throttlevalve 52 to the production fluid outlet 54 and through the productionpipeline 18 to the host facility for processing.

[0044] A control system (not shown) receives signals from the levelsensor 56 and a pressure sensor 78 and controls the throttle valves 40and 52 and the recirculation pump 38 to maintain the interface betweenthe fluids in the chamber 32 at the required level and the overallpressure in the chamber 32 at an appropriate level. For example, if theamount of jetting fluid in the chamber 32 needs to be increased, thethrottle valve 40 will be closed slightly in order that jetting fluidwill be forced through the recirculation loop pipe 46 back into thechamber 32.

[0045] Accordingly, the same batch of jetting fluid will be cycledrepeatedly between the jet pump 14 and the separation facility 6. Hence,in the case of local seawater being deemed unacceptable for the purposeonly a relatively small bore pipe 20 will be required for delivering theinitial batch of jetting fluid to the separation facility 6 and theproduction pipeline 18 does not need to be unnecessarily enlarged so asto accommodate a flow of jetting fluid in addition to production fluid.Furthermore, any tariff charged by the host facility owner will only bein respect of production fluid delivered thereto and will not beincreased as a consequence of delivering jetting fluid thereto.

[0046] While the invention has been described in the context of a subseahydrocarbon field, it would also be applicable to other areas whereaccess posed a problem, for example in swampy areas or remote locations.

1. A method of boosting production from a wellbore (4) having a downholejet pump (14) and a remote host facility (16), the method comprising thesteps of: (a) providing a separation facility (6) substantially closerto the wellbore (4) than the host facility (16); (b) providing means(38, 68, . . . ) to deliver jetting fluid (60) under pressure to the jetpump (14); (c) entraining wellbore production fluid with the flow of thejetting fluid in the jet pump (14) and conveying the resulting mixtureto the separation facility (6); (d) separating a majority of the jettingfluid (60) from the mixture by means of the separation facility (6); and(e) recirculating the separated jetting fluid (60) back to the jet pump(14) and entraining further production fluid therewith.
 2. The methodaccording to claim 1 wherein at least 90% of the jetting fluid (60) isseparated from the mixture by the separation facility (6).
 3. The methodaccording to claim 2 wherein substantially all of the jetting fluid (60)is separated from the mixture by the separation facility (6).
 4. Themethod according to any preceding claim wherein the separation facility(6) is situated at or close to the wellbore (4).
 5. The method accordingto any preceding claim wherein the separation facility (6) includes apump (38) which is used to pressurise separated jetting fluid (60) forassisting its recirculation.
 6. The method according to any precedingclaim wherein the separation is effected by gravity separation.
 7. Asystem for boosting production from a wellbore (4) situated remotelyfrom a host facility (16) comprising a downhole jet pump (14),pressurising means (38, 68) for supplying the jet pump (14) withpressurised jetting fluid (60) for forming a mixture of jetting fluid(60) and wellbore production fluid, a separation facility (6) situatedsubstantially closer to the wellbore (4) than the host facility (16)including separation means (22, 24) for separating a majority of thejetting fluid (60) from the mixture and recirculation means (10, 12, 38,39) for delivering the separated jetting fluid (60) back to the jet pump(14) for entraining further production fluid therewith.
 8. The systemaccording to claim 7 wherein the separation means (22, 24) includes atleast one gravity separation chamber (32).
 9. The system according toclaim 7 or 8 wherein the separation means (22, 24) includes at least twoseparators (32) for separating the mixture which are connected inparallel with each other.
 10. The system according to claim 7, 8 or 9wherein the separation means (22, 24) includes throttling means (40, 52)arranged to control flows of production fluid and jetting fluid (60)from the separation means (22, 24).